1. Field of the Invention
The present invention is generally directed to storage devices and, more specifically, to a tank or reservoir particularly designed for storing liquid products below the ground surface which is provided with an outer anticorrosion protective cover for efficiently controlling and monitoring an eventual leakage of the stored liquid. Under another aspect, the present invention is directed to a process for the manufacture of such underground reservoir having an outer anticorrosion protective layer.
2. Description of the Prior Art
A problem with tanks or reservoirs used for storing liquid products at a level below the ground surface, such as those used in fuel sale stations, is that they are frequently structurally deteriorated in view of the aggressive environment in which the same are used.
Indeed, the relatively high corrosion degree of the environment surrounding the tank attacks the material from which the reservoir is manufactured and tends to speed up the corrosion thereof, resulting in a general degradation of its structure which may lead to the occurrence of leaks.
An underground reservoir structurally corroded, besides allowing the leakage of the product stored inside same and, as a consequence, the inadmissible contamination of the surrounding environment, thus increasing the well known risks of pollution, can allow the water to infiltrate into same, what can hamper the quality of the product being commercialized.
Since the costs related to the replacement of such an underground reservoir for storing liquid products can be prohibitively high, without mentioning the problems resulting from the required partial interruption of the traffic along the surface roads close to the place where the same is being installed, a regular replacement of such reservoirs is unfeasible.
A solution which has previously been attempted to solve the foregoing problem was the installation of continuous cathodic protection anodes, such as cable, tape and tubular anodes, buried close to the underground metallic structures such as pipes or storage tanks for protecting same against corrosion.
The anodes provide protection for the reservoir by increasing the electric potential of the ground surrounding same through the application of a direct current to the anode and the ground at a potential enough to keep the reservoir under a negative voltage with relation to the anode and, thus, to protect the metallic surface of the reservoir against any attack.
Typically, the anode is encapsulated in a carbon material such as powdered coke particles to increase the flow of the input current. The anodes are flexible and deemed to be “continuous” in view of the fact that they are elongated and tubular in shape, and can be laid along the reservoir.
This solution, however, is too much expensive and does not fully eliminate the problem of corrosion caused by chemicals on the outer metallic surface of the underground reservoir being used as a supplementary protection means against corrosion in grounds having a high potential.
Another solution previously proposed to address the problem of the attack against the inner and outer walls of the reservoirs was the manufacture of coated or jacketed tanks or reservoirs, that is, having an inner or primary compartment for storing the liquid product and an outer or secondary compartment having slightly larger inner dimensions than those of the inner reservoir, the purpose of which is to function as a protection shield for the inner reservoir.
Typically, in accordance with the constructive dispositions known in the state of the art, such coated or jacketed reservoirs are comprised of tanks having a double steel-steel wall comprising an inner reservoir made from carbon steel in the interior of which the liquid product is stored, and an outer reservoir which is also made from carbon steel and serves as a protection against the corrosion of the main reservoir by agents from the ground and also as a containment barrier in the event of a leakage. There is a minimum gap (interstice) between the two tanks within which a sensor for detecting the presence of liquids is installed on its lowermost point, in order to monitor any leakage that may eventually take place.
Another solution mostly used in view of its lower cost than that of the double steel walls tank is the use of a coated or jacketed reservoir in which the outer or secondary tank is made from fiberglass.
However, such coated or jacketed reservoirs in accordance with the known state of the art present several technical and/or functional disadvantages, among which the following ones can be cited:
The jacketed reservoirs provided with double steel walls are too heavy, thus making the installation of same difficult and expensive due to the need of using larger capacity lifting devices (cranes).
Another problem of such jacketed reservoirs provided with double steel walls is that the process for manufacturing same is laborious and the time for producing same is too long.
The drawback of such coated or jacketed reservoirs provided with double walls made from steel and fiberglass is the fact that the production process involving fiberglass is unhealthy and dangerous because of the toxic and explosive/flammable nature of the materials used in this process, such as acetone, catalysts and aromatic compounds, and thus the whole industrial process should be dealt with carefully, from the storage of raw materials to its application, what should be made in a place provided with an exhaustion and fire-fighting system.